Compression and injection molded plastic closures are widely used in the marketplace on associated containers, including both carbonated and non-carbonated beverages. Compression molded sealing liners, as well as pre-formed insertible liners, are commonly put in place in the closure after the closure has been formed. U.S. Pat. Nos. 4,807,772 and 4,846,362 disclose liner compositions made of a blend of polyethylene or polypropylene and thermoplastic elastomeric copolymer.
Conventional liner resin compositions typically contain significant amounts of ethylene vinyl acetate (EVA) copolymer. For example, U.S. Pat. No. 4,984,803 discloses a sealing liner wherein EVA comprises about 70% of the liner composition.
Conventional closure liners are also described in, for instance, U.S. Pat. No. 5,104,710, EP 0478109, EP 0599356, EP 0488491, and 0646158. The liners may be applied to the closure by any of the known methods, such as those described in, for example, U.S. Pat. No. 4,518,336, EP 207385, and U.S. Pat. No. 4,277,431. The disclosures of the above-mentioned patents are herein incorporated by reference in its entirety.
Experience has shown that there are certain drawbacks associated with using EVA-containing liner resin compositions. For example, EVA-containing liner resin compositions have a relatively narrow processing window which can result in high levels of molding defects, such as large/ballooning bubbles, flash, non-fills and the like. Also, resins that contain EVA copolymer may limit the molding speed at which liners are molded into closures. In addition, non-EVA liner resin compositions may reduce the amount of resin needed to form a functional liner.
Thus, there is a need for novel liner resin compositions without substantial amounts of EVA.